A mobile radio network covers a geographical area which is divided into cell areas, wherein each cell area being generally served by a radio network node. A radio network node may be a Radio Base Station (RBS), also sometimes referred to as e.g. “eNB”, “eNodeB”, or BTS (Base Transceiver Station) depending on which part of the technology needs to be referred. A radio network node or RBS may provide radio coverage to one or more cells. Further, each radio network node may support different communication technologies e.g. Time Division Duplex, TDD, Frequency Division Duplex, FDD. The radio network nodes communicate with user equipments (UEs) also referred to as mobile stations, mobile terminals, wireless terminals, mobile telephones, cellular telephones or smartphones situated within its radio network cell. Other examples of UEs are laptops, notebooks, tablets, handheld devices. All of those having wireless communication capabilities. In addition, a radio mobile communication may be performed between two or more UEs, two or more radio network nodes or two or more radio network core nodes. All of the above-mentioned pieces form part of a radio mobile network.
When the communication is performed between two user equipments, each of these equipments communicates within a frequency band or channel allocated to one operator in a radio network. The frequency band may be a whole spectrum chunk whilst a channel may be a subset of the spectrum resources of the frequency band used for resource management purposes.
Furthermore, the frequency bands in Long Term Evolution (LTE) may operate in both paired and unpaired spectrum, requiring flexibility in the duplex arrangement.
The 3rd Generation Partnership Project (3GPP) provides LTE and “System Architecture Evolution” (SAE) and defines Evolved Packet System (EPS). EPS consists of the evolved Radio Access Network (EUTRAN) and the Evolved Packet Core (EPC).
In this disclosure, a radio network core node may relate to nodes in the evolved packet core (EPC). These nodes may be Mobility Management Entity (MME), Serving Gateway (SGW), Packet Data Network (PDN) Gateway (PGW) or Home Subscriber Server (HSS) and in the 3GPP LTE, the radio network nodes may be directly connected to one or more network core nodes.
Other radio mobile networks that may be used in this disclosure are e.g. Global System for Mobile Communications (GSM), the GSM-evolved Universal Mobile Telecommunications System (UMTS) and UMTS based on Wideband Code Division Multiple Access (WCDMA) for mobile systems, HSPA, WiMax.
Cell-Connectivity
In terms of 3GPP LTE network, a UE can transmit or receive information from this network by searching and selecting an appropriate serving cell, obtaining basic system information and performing random access. By doing this, a UE can obtain synchronization, system parameters and access to system resources.
Device-to-Device Communication
D2D communication allows exploiting the proximity between D2D-capable user equipments. This involves lower power consumption, lower end-end delays and eventually higher data rates that make D2D technology suitable for bandwidth-demanding services such as video streaming, gaming applications and fast data transfer between devices. In addition, D2D is implicitly tailored for proximity-based social networking services and information broadcasting applications.
There are many aspects where D2D communications may take place and some of them are shown in FIG. 1.
There are those that communicate with licensed spectrum and others with unlicensed spectrum. Various ad hoc and personal area networking technologies utilize unlicensed spectrum bands such as the industrial, scientific and medical bands which are available for short range communications, including Bluetooth and WiFi Direct.
On the other hand, D2D communication with licensed spectrum has only recently been proposed and studied. According to this concept, UEs in the proximity of each other can exchange information over a direct link rather than transmitting and receiving signals through a radio base station (eNB) or radio network node. The problem associated with these techniques is that the UEs need to be situated within a radio cell (here also referred as to a radio network) and cannot cross boundaries into other operator licensed/unlicensed frequency bands. This is because at present there are no available inter-operator licensed/unlicensed frequency bands. Furthermore, the allocation of those frequency bands would require lengthy standardization and regulatory processes.
Establishing a direct D2D communication assisted by a network infrastructure such as 3GPP LTE is possible to improve the utilization of cellular spectrum resources and to reduce the energy consumption of user equipments. The assistance may involve neighboring discovery, resource allocation, power control and mode selection policies. The potential gains of D2D communications are equally attractive in cellular networks operated in paired as well as unpaired frequency bands. In the 3GPP LTE system, for example, the FDD and TDD modes are specified in the same set of specifications for both the UE and the eNB. In other words, the D2D communication based on LTE is generally supported in cellular networks operated in either of the duplexing modes. However, existing logical interfaces e.g. X2 Interface do not allow communication between radio network nodes (eNBs) belonging to different operators or radio networks with different duplexing modes. One solution would be for a UE in a operator or radio network to roam into the neighboring radio network or other operator in order to enable D2D communication with a UE in that network. However national roaming is generally not allowed due to regulatory reasons. In addition, a D2D-capable UE that performs roaming could suffer from limited connection due to the potential high distance from the radio network nodes of other radio networks.